Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Mg-based Alloy for Hydrogen Storage
Field of the invention
This invention relates to a Mg-based alloy capable of being formed by
conventional
melting and casting techniques and which is suitable for use as a metal
hydride-based
material suitable for the storage and transportation of hydrogen in the solid
state. The
disclosed Mg-based alloy has controlled additions of one or more of the
following
elements: Cu, Na, Ni, and Si. Based on a close understanding of the role
played by
each element, it is possible to tailor the alloy to achieve a favourable
combination of
performance attributes, providing attractive hydrogen storage properties
compared with
other cost-comparable and weight-comparable hydrogen storage materials.
Background of the invention
As well as being an important industrial gas used in various industrial
processing
applications, hydrogen is also being seen as an important alternative energy
source to
carbon-based fossil fuels. The need for safe and suitable storage and
transportation
devices for hydrogen is therefore increasing. Existing technologies for
storing and
transporting hydrogen require either: high compression pressures and heavy
steel gas
cylinders to store hydrogen as a gas, or, extremely low cryogenic temperatures
and
expensive thermally insulated vessels to store hydrogen as a liquid. Both of
these have
implicit safety issues. The concept of storing hydrogen gas via a chemical
reaction with
a suitable solid such that the gas is effectively occluded into the solid and
rendered
significantly safer is extremely attractive, and much effort has been expended
to find a
suitable storage material.
It is well known that Mg is capable of storing hydrogen as magnesium hydride
(MgH2) at
7.6 mass%. However, the kinetics of the absorption and desorption reactions
for pure
Mg are too slow for it to be of practical use as a solid state hydrogen
storage material.
Various methods have been used to improve the adsorption/desorption kinetics
of Mg,
and hence its practical applicability for use as a storage material. These
include one or
more of the following approaches: addition of specific elements to provide
catalytic
benefits (for example, Ni); addition of specific elements to provide a
beneficial
secondary phase (for example, Zr); refining the microstructure by mechanical
means
(for example, by ball-milling); refining the microstructure by thermal means
(for example,
by rapid solidification techniques like melt-spinning); and, producing an
amorphous
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glassy phase by a combination of composition control and thermal means (for
example,
by high levels of alloying additives combined with rapid cooling rates).
The practical applications for hydrogen storage and transportation systems are
many
and varied and will continue to emerge and evolve over time. The differing
applications
are likely to require, or at least be able to benefit from differing
combinations of
hydrogen storage performance characteristics, for example, longer or shorter
activation
times, faster or slower absorption rate, faster or slower desorption rate.
This may be
further coupled with the considerations of relative weight (e.g. mass of H2
stored/mass
of storage alloy and equipment) and relative cost (mass of H2 stored/cost of
storage
alloy and equipment) to convert potential applications into viable commercial
realities.
One of the ways to control an alloy's performance, weight and cost is through
the
deliberate tailoring of the alloy composition. In order to do this, it is
important to avoid
the use of exotic and expensive elements, and of heavy dense elements, in the
preferred alloy formulations.
It is also highly desirable that the alternative alloy compositions can be
produced
economically by commercial casting techniques, rather than expensive and
complex
formation technologies, such as ball-milling or vapour deposition, that are
frequently
proposed in the prior art.
It is also desirable that such simply produced alloys require no further post
processing
actions apart from mechanical fragmentation of the solidified cast alloy to
transform it
into loose packable material, such as chips or granules.
In general, elements can be classified as being either "eutectic-forming",
"peritectic-
forming" or "monotectic-forming" with respect to another element species. In
this patent
application, our main interest is with certain elemental additions that are
"eutectic-
forming" with Mg (this concept is described below). The elements that are
known to
form "binary" eutectics with Mg are: Al, Ag, Au, Ba, Bi, Ca, Ce, Cu, Eu, Ga,
Gd, Ge, Hg,
La, Ni, Pb, Sb, Si, Sm, Sn, Sr, Th, TI, Y, Yb and Zn. Of these, we focus on
only three of
these: Cu, Ni and Si. (Note: Na is monotectic-forming with Mg, not a eutectic-
forming.)
When an element E that is added to another element (such as Mg in our case)
forms a
eutectic with the latter element, it is termed a eutectic-forming element. A
eutectic is a
mixture of two (or more) distinct constituent phases in distinct proportions
and with
distinct structures. Where a eutectic consists of only two elements and two
constituent
phases it is called a binary eutectic. A eutectic always has a lower melting
point than the
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two (or more) individual constituent phases that make up the eutectic. The
eutectic point
is a uniquely defined condition of temperature and alloy composition.
If the eutectic-forming element E is added to another element at an amount
that is less
than the amount required to attain the eutectic composition of that alloy
system, it is
said to be an alloy of hypoeutectic composition. Eutectic compositions are
well
documented in the general literature for almost all two-element alloy systems.
In the
case of element E being added to molten Mg at a hypoeutectic amount, this will
result,
upon cooling, in the formation of a Mg solid solution phase first (that is,
primary Mg)
before the formation of a dual-phase eutectic (a mixture of Mg and an MgxEy
intermetallic, where x, y are values determined by the individual phase's
atomic and
crystalline features).
If the eutectic-forming element E is added at a higher composition than that
required to
attain the eutectic composition, it is said to be an alloy of hypereutectic
composition,
and in the case of element E being added to Mg, this will result in the
formation of
MgxEy intermetallic first (that is, primary MgxEy intermetallic) prior to the
formation of the
dual-phase eutectic (as noted above).
The distinction between hypoeutectic and hypereutectic alloy compositions is
important
as the first phase to form determines the main structural skeleton (that is,
as crystals,
grains or particles) of the alloy, with the eutectic subsequently filling in
the gaps in
between this primary structure. An alloy structure consisting of a skeleton of
primary Mg
solid solution is therefore metallurgically different in a substantial way
from a structure
consisting of a skeleton primary MgxEy intermetallic.
Reference to any prior art in the specification is not, and should not be
taken as, an
acknowledgment or any form of suggestion that this prior art forms part of the
common
general knowledge in Australia or any other jurisdiction or that this prior
art could
reasonably be expected to be ascertained, understood and regarded as relevant
by a
person skilled in the art.
Summary of the invention
The inventors have discovered a range of alloys of Mg and at least one of Cu,
Si, Ni and
Na alloys that is particularly suitable for hydrogen storage applications. The
alloys are
essentially hypoeutectic with respect to their Cu and Ni contents, where one
or both of
these elements are present, but range from hypoeutectic through to
hypereutectic with
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respect to their Si content when that element is also present. The terms
hypoeutectic
and hypereutectic do not apply to Na if it is added to the alloy.
The alloy compositions disclosed provide high performance alloys with regard
to their
hydrogen storage and kinetic characteristics. They are also able to be formed
using
conventional casting techniques which are far cheaper and more amenable to
commercial use than the alternative ball-milling and rapid solidification
techniques which
are much more expensive and complex.
Each of the individual binary Mg-E systems, where E = Cu, Ni or Si, forms a
eutectic
comprising of Mg metal and a corresponding MgxEy intermetallic phase (Figures
1-3). In
addition to the ability of Mg metal to absorb hydrogen to form the hydride
MgH2, each of
the MgxEy intermetallic phases is also able to absorb hydrogen to various
degrees to
form corresponding hydrides of the form MgaEbH,, or similar.
Note that the other element of interest, Na, does not form a eutectic with Mg,
instead it
forms a monotectic and exhibits a miscibility gap, meaning that essentially
pure
elemental Na co-mingles with Mg in which only a small amount of Na is able to
be
dissolved. This leaves the Na free to interact with the alloy in several
possible and
interesting ways that are described in detail later.
In a first aspect of the invention there is provided a Mg-Cu based alloy that
is able to be
formed by commercial casting methods and which is suitable for hydrogen
storage
applications and which consists essentially of:
i. an amount of Cu such that the alloy is hypoeutectic with respect to Cu
content, that is greater than zero and less than 32 mass% Cu; more
preferably with Cu content between 0.1 mass% and 9 mass%; and, most
preferably Cu between 0.1 mass% and 5.5 mass%; and optionally an amount
of Ni such that the alloy is hypoeutectic with respect to Ni content, that is
zero
or greater than zero and less than 23.5 mass% Ni;
ii. an amount of Na from zero and up to 2 mass% Na (20,000 ppm, that is,
parts
per million), more preferably at a level between 200 and 4,000 ppm; and,
most preferably a level between 800 and 2,000 ppm;
iii. incidental impurities totalling less than 0.5 mass%; and
iv. the balance of the alloy mass being Mg,
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the alloy having a primary (initially formed) crystallized Mg phase and a
subsequently crystallized Mg-Cu based eutectic.
In a second aspect of the invention, there is provided a Mg-Si based alloy
that is able to
be formed by commercial casting methods and which is suitable for hydrogen
storage
applications and which consists essentially of:
i. (a) an amount of Si such that the Mg-Si alloy is hypoeutectic
with respect to
Si content, that is greater than zero and less than 1.34 mass% Si; or
(b) an amount of Si such that the alloy is hypereutectic with respect to Si
content, that is greater than 1.34 mass% and less than 36.6 mass% Si;
ii. optionally at least one of an amount of Ni such that the alloy is
hypoeutectic
with respect to Ni content, that is zero, greater than zero and less than 23.5
mass% Ni; and an amount of Cu such that the alloy is hypoeutectic with
respect to Cu content, that is zero, greater than zero and less than 32
mass% Cu;
iii. an amount of Na from zero and up to 2 mass% Na (20,000 ppm),more
preferably at a level between 200 and 4,000 ppm; and, most preferably a
level between 800 and 2,000 ppm;
iv. incidental impurities totalling less than 0.5 mass%, ; and
v. the balance of the mass being Mg,
the alloy having a primary crystallized Mg phase and a subsequently
crystallized Mg-Si based eutectic.
A third aspect of the invention provides the above Mg-Si based alloy of the
second
aspect where
the amount of Si is such that the alloy is hypereutectic with respect to Si
content.;
and
optionally consists of at least one of an amount of Ni such that the alloy is
hypoeutectic with respect to Ni content, that is zero or greater than zero and
less than 23.5 mass% Ni; and an amount of Cu such that the alloy is
hypoeutectic with respect to Cu content, that is zero or greater than zero and
less than 32 mass% Cu;
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the alloy having primary crystallized Mg2Si intermetallic phase and a
subsequently
crystallized Mg-Si based eutectic.
A fourth aspect of the invention provides the Mg-Si alloy of the second aspect
where
the amount of Si is such that the alloy is hypoeutectic with respect to Si
content,
that is greater than zero and less than 1.34 mass% Si; more preferably with
Si content between 0.1 mass% and 1.34 mass%; and, most preferably Si
between 0.2 mass% and 1.34 mass%; and
optionally at least one of an amount of Ni such that the alloy is hypoeutectic
with
respect to Ni content, that is zero or greater than zero and less than 23.5
mass% Ni and an amount of Cu such that the alloy is hypoeutectic with
respect to Cu content, that is zero or greater than zero and less than 32
mass% Cu.
A fifth aspect provides a Mg-Cu-Ni based alloy consisting essentially of the
Mg-Cu alloy
of the third aspect having
amount of Ni being such that the alloy is hypoeutectic with respect to Ni
content,
that is greater than zero and less than 23.5 mass% Ni; more preferably with
Ni content between 0.1 mass% and 9 mass%; and, most preferably Ni
between 0.1 mass% and 5.5 mass%;
the alloy having a primary crystallized Mg phase and a subsequently
crystallized
mixture of one or more of Mg-Cu based eutectic, Mg-Ni based eutectic and
Mg-Cu-Ni based eutectic.
In a sixth aspect of the invention, there is provided a Mg-Cu-Si based alloy
consists
essentially of the Mg-Si alloy of the fourth aspect having
an amount of Cu is such that the alloy is hypoeutectic with respect to Cu
content,
that is greater than zero and less than 32 mass% Cu; more preferably with
Cu content between 0.1 mass% and 7 mass%; and, most preferably Cu
between 0.1 mass% and 4.5 mass%; and
an amount of Na from zero and up to 2 mass% Na (20,000 ppm); more preferably
at a level between 200 and 4,000 ppm; and, most preferably a level between
800 and 2,000 ppm;
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the alloy having a primary crystallized Mg phase and a subsequently
crystallized
mixture of one or more of Mg-Cu based eutectic, Mg-Si based eutectic and
Mg-Cu-Si based eutectic.
In a seventh aspect of the invention there is provided a Mg-Cu-Si based alloy
which
consists essentially of the Mg-Si alloy of the third aspect where the
an amount of Cu such that the alloy is hypoeutectic with respect to Cu
content,
that is greater than zero and less than 32 mass% Cu; more preferably with
Cu content between 0.1 mass% and 7 mass%; and, most preferably Cu
between 0.1 mass% and 4.5 mass%;
an amount of Na from zero and up to 2 mass% Na (20,000 ppm); more preferably
at a level between 200 and 4,000 ppm; and, most preferably a level between
800 and 2,000 ppm;
and optionally an amount of Ni such that the alloy is hypoeutectic with
respect to
Ni content, that is zero, greater than zero and less than 23.5 mass% Ni;
the alloy having a primary crystallized Mg2Si intermetallic phase and a
subsequently crystallized mixture of one or more of Mg-Cu based eutectic,
Mg-Si based eutectic and Mg-Cu-Si based eutectic.
In an eighth aspect of the invention there is provided a Mg-Ni-Si based alloy
which
consists essentially of the Mg-Si alloy of the fourth aspect where
the amount of Ni is such that the alloy is hypoeutectic with respect to Ni
content,
that is greater than zero and less than 23.5 mass% Ni; and
an amount of Si such that the Mg-Ni-Si alloy is hypoeutectic with respect to
Si
content, that is greater than zero and less than 1.34 mass% Si;
an amount of Na from zero and up to 2 mass% Na (20,000 ppm); more preferably
at a level between 200 and 4,000 ppm; and, most preferably a level between
800 and 2,000 ppm; and
optionally an amount of Cu such that the alloy is hypoeutectic with respect to
Cu
content, that is zero or greater than zero and less than 32 mass% Cu;
the alloy having a primary crystallized Mg phase and a subsequently
crystallized mixture of one or more of Mg-Ni based eutectic, Mg-Si based
eutectic and Mg-Ni-Si based eutectic.
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In a ninth aspect of the invention there is provided a Mg-Ni-Si based alloy
which
consists essentially of the Mg-Si alloy of the third aspect where
the amount of Ni is such that the alloy is hypoeutectic with respect to Ni
content,
that is greater than zero and less than 23.5 mass% Ni; more preferably with
Ni content between 0.1 mass% and 7 mass%; and, most preferably Ni
between 0.1 mass% and 3.5 mass%;
the alloy having a primary crystallized Mg2Si intermetallic phase and a
subsequently crystallized mixture of one or more of Mg-Ni based eutectic,
Mg-Si based eutectic and Mg-Ni-Si based eutectic.
In a tenth aspect of the invention there is provided a Mg-Cu-Ni-Si based alloy
which
consists essentially of the Mg-Ni-Si alloy of the ninth aspect where
the amount of Cu is such that the alloy is hypoeutectic with respect to Cu
content,
that is greater than zero and less than 32 mass% Cu; more preferably with
Cu content between 0.1 mass% and 7 mass%; and, most preferably Cu
between 0.1 mass% and 4.5 mass%; and
the amount of Ni is such that the Mg-Cu-Ni-Si alloy is hypoeutectic with
respect to
Ni content, that is greater than zero and less than 23.5 mass% Ni; more
preferably with Ni content between 0.1 mass% and 7 mass%; and, most
preferably Ni between 0.1 mass% and 4.5 mass%;
the alloy having a primary crystallized Mg phase and a subsequently
crystallized
mixture of one or more of Mg-Cu based eutectic, Mg-Ni based eutectic, Mg-
Si based eutectic, Mg-Cu-Si based eutectic, Mg-Cu-Ni based eutectic, Mg-Ni-
Si based eutectic and Mg-Cu-Ni-Si based eutectic.
In an eleventh aspect of the invention there is provided a Mg-Cu-Ni-Si based
alloy
which consists essentially of the Mg-Cu-Si alloy of the seventh aspect
the amount of Ni is such that the Mg-Cu-Ni-Si alloy is hypoeutectic with
respect to
Ni content, that is greater than zero and less than 23.5 mass% Ni; more
preferably with Ni content between 0.1 mass% and 7 mass%; and, most
preferably Ni between 0.1 mass% and 4.5 mass%;
the alloy having a primary crystallized Mg2Si phase and a subsequently
crystallized mixture of one or more of Mg-Cu based eutectic, Mg-Ni based
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eutectic, Mg-Si based eutectic, Mg-Cu-Si based eutectic, Mg-Cu-Ni based
eutectic, Mg-Ni-Si based eutectic and Mg-Cu-Ni-Si based eutectic.
Table 1 provides a table of important alloy system data pertaining to
individual Mg-Cu,
Mg-Ni and Mg-Si binary eutectic systems. From this data, those skilled in the
art can
determine for any given composition, the types, compositions and amounts of
the
primary Mg, primary intermetallic and secondary eutectic phases (both the Mg
and
corresponding intermetallic constituents) that will form during the
solidification of the
alloy. Thus, by choice of composition it is possible to design an alloy
composition to
contain specific amounts (either by mass% or volume%) of Mg and each type of
binary
intermetallic (assuming the binary eutectics form more or less independently
of each
other, and that ternary eutectic formation does not dominate in the alloy
system).
Each of the elements noted above have their own different effects on the
hydrogen
storage properties of Mg and its alloy derivatives. In addition, each element
carries its
own weight benefit or penalty (since they each affect alloy density) and its
own cost
benefit or penalty per percentage point of the element added. Knowledge of
these
effects allows for tailoring of alloy composition to meet the requirements of
specific
applications. Some of the discovered elemental effects on hydrogen storage
properties
are as follows:
The presence of Ni in Mg shortens the activation time required before hydrogen
begins
to be absorbed, that is, for the alloy to become activated. It also increases
the hydrogen
absorption and desorption rates during repeated cycling. However, it is noted
that Ni is
a relatively expensive element that is subject to price volatility.
The presence of Cu in Mg has been discovered to improve the overall hydrogen
absorption rate during the first hour of each repeated absorption/desorption
cycles,
compared to an equivalent addition amount of Ni (Figure 4), but to impair the
hydrogen
desorption rate (Figure 5). For applications where desorption rate is non-
critical, Cu, as
a cheaper metal than Ni, offers the potential for reduced alloy cost compared
to Ni, and
thus the opportunity to tailor the storage material composition such that the
economics
of the specific application are improved and made more commercially viable.
The presence of Si in Mg provides some improvement in activation time but in
the
binary alloy system the hydrogen storage capacity remains low compared to
additions
of Cu and Ni, unless Na is also added in which case both activation time and
storage
capacity are improved to acceptable levels for less demanding performance
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applications. Furthermore, because Si is much lighter and cheaper than either
Cu or Ni,
and since it is capable of forming large amounts of beneficial eutectic phase
even at low
addition levels, for example, below 1.34 mass% (the eutectic composition, see
Table 1),
Mg-Si alloys potentially lend themselves to applications where weight and cost
reductions are paramount.
It has further been found that the presence of Si in Mg-Ni alloy (with or
without Na),
even at levels below 1.34 mass%, improves hydrogen storage capacity in low Ni
content alloys. This effect appears to be due to its influence on
microstructure (Figure
6), the large amounts of Mg2Si intermetallic increasing the diffusion pathways
for
hydrogen atoms within the Mg grains. We have also discovered that the presence
of Si
in Mg-Cu alloy with various Cu contents, even at levels below 1.34 mass%,
improves
hydrogen storage capacity.
The alloy structures and compositions claimed above (and tabulated in Table 2)
are
capable of providing alloy hydrogen storage characteristics that are
comparable to or
better than those obtained using ball-milled Mg-alloy material, in particular
when
considered from an economic perspective.
Table 1 - Important alloy system data for Cu, Ni and Si added to Mg
Max. solid Eutectic Amount of E
Intermetallic in
Added solubility of composition
formed in intermetallic
Element (E) E in Mg (mass % of
eutectic
(mass %) E) (mass %)
Cu - 0 32.0 Mg2Cu 56.7
Ni - 0 23.5 Mg2Ni 54.7
Si -0 1.34 Mg2Si 36.6
Table 2 - Ranges of alloying element additions claimed in the invention
More
Most preferred
Added with other Max. range preferred
range (mass
Element (E) elements (mass %) range (mass
%)
%)
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alone; 1 - 9 2 - 6
Cu +Ni; >0 - 32.0 0.1 -9 0.1 ¨5.5
+Si; +Ni+Si 0.1 -7 0.1 -4.5
+Cu; 0.1 -9 0.1 -5.5
Ni >0 - 23.5
+Si; +Cu+Si 0.1 -7 0.1 ¨4.5
alone >0 ¨ 1.34
+Cu; +Ni;
Si (hypo)>0 - 1.34 0.1 ¨ 1.34 0.2 ¨ 1.34
+Cu+Ni
alone; +Cu;
Si (hyper) 1.34 ¨ 36.6 1.34 ¨ 7 1.34 ¨ 3.5
+Ni; +Cu+Ni
0 ¨ 20,000 200 ¨ 4,000 800 ¨ 2,000
Na any comb'n
ppm ppm ppm
Note: In Table 2, three eutectic-forming elements (Cu, Ni and Si) are
considered in
various combinations. Na is not a eutectic-forming element, but may be added
to any of
the element combinations listed to achieve various outcomes. In all cases, Mg
forms the
balance of the alloy composition, with the exception of up to 0.5% impurities.
Each of the above claimed alloys containing one or more of the eutectic-
forming
elements, Cu, Ni and Si, is capable of acting as a hydrogen storage alloy but
we have
further discovered that the hydrogen storage performance of each may be
further
enhanced by the presence of Na addition which appears to perform one or more
of
several functions. For example, Na improves activation performance and alloy
processing characteristics. Not wishing to be bound by theory, it may achieve
these
affects by:
= Refining the microstructure of the eutectic;
= Altering the nature of the oxide surface that develops on the alloy,
thereby
affecting the hydrogen transfer rate across the alloy-gas interface;
=
Providing its own catalytic function in terms of enhanced hydrogen kinetics,
independent of that provided by any of the other elements;
= Providing a Na-enriched layer around grains and in the interdendritic
spaces
that enhances transport of hydrogen through the alloy; or
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= Providing a layer (as above) that causes brittleness in the alloy and
which in
turn enhances the mechanical fragmentation of the alloy to a fine scale, thus
improving transport of hydrogen through the alloy by a different means.
The alloy invention is described in more detail in a subsequent section.
Brief Description of the Drawings
Figure 1 is a Mg-Cu binary phase diagram;
Figure 2 is a Mg-Ni binary phase diagram;
Figure 3 is a Mg-Si binary phase diagram;
Figure 4 is a graph of hydrogen absorption curves at 4th test cycle for some
of the alloys
described in examples 2, 6 and 7 (see Table 3 also);
Figure 5 is a graph of hydrogen desorption curves at 4th test cycle for some
of the alloys
described in examples 2, 6 and 7 (see Table 3 also); and,
Figure 6 is a micrograph (SEM) showing the microstructure of a Mg-5.3%Ni-
0.34%Si-
0.093%Na alloy showing the presence of two distinct eutectic structures.
Detailed Description of the Embodiments
The alloy compositions disclosed provide high performance alloys with regard
to their
hydrogen storage and kinetic characteristics. They are also able to be formed
using
conventional casting techniques which are far cheaper and more amenable to
commercial use than the alternative ball-milling and rapid solidification
techniques which
are much more expensive and complex.
Each of the individual binary Mg-E systems, where E = Cu, Ni or Si, forms a
eutectic
comprising of Mg metal and a corresponding MgxEy intermetallic phase (Figures
1-3). In
addition to the ability of Mg metal to absorb hydrogen to form the hydride
MgH2, each of
the MgxEy intermetallic phases is also able to absorb hydrogen to various
degrees to
form corresponding hydrides of the form MgaEbH,, or similar.
The alloy structures and compositions described above (and illustrated in
Table 2) are
capable of providing alloy hydrogen storage characteristics that are
comparable to or
better than those obtained using ball-milled Mg-alloy material. In particular,
in terms of
specific test values such as effective peak hydrogen (EPH), expressed in mass%
H2.
This value is measured after repeated absorption and desorption cycles,
typically four
cycles, carried out at approximately 350 C/10-15 bar and 350 C/1-2 bar,
respectively.
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(Note: other important test values include the initial activation time, that
is, the delay or
incubation period before hydrogen absorption starts to occur during the first
test cycle,
and the saturation hydrogen level achieved after the initial 20 hour period.)
These
excellent hydrogen storage characteristics are achieved without the use of
expensive
and exotic elemental additions such as Pd, without the need for very high
addition levels
of Ni and Cu into the hypereutectic range, and without the need for complex
and
expensive alloy forming methods. Rather, each of the claimed alloys
compositions is
capable of being made using conventional casting techniques.
The alloy compositions described and claimed are also capable of providing
hydrogen
absorption and desorption rates that differ from those of Mg-Ni-Na alloy, thus
allowing
the compositions of the alloys to be tailored to performance levels suitable
for specific
applications, and which are superior on a weight-for-weight basis, or a cost-
for-cost
basis cost, or to some other similar customer-based or production-based
comparative
parameter.
Certain Mg alloys that contain eutectic forming elements, such as Ni, have far
superior
hydrogen storage characteristics compared to pure Mg metal. It has
consequently been
found that it is the presence of the eutectic intermetallic phases, for
example Mg2Ni, that
provide this benefit by: acting as catalysts for hydrogen storage in Mg,
providing
alternative hydriding phases, and/or providing easy physical pathways for the
transport
of hydrogen atoms.
Given this understanding it is not surprising that one skilled in the art
might predict that
any of the eutectic forming elements (that is, Al, Ag, Au, Ba, Bi, Ca, Ce, Cu,
Eu, Ga, Gd,
Ge, Hg, La, Ni, Pb, Sb, Si, Sm, Sn, Sr, Th, TI, Y, Yb and Zn) or combinations
thereof
should substantially improve the hydrogen storage characteristics of Mg.
However, this is not the case as is demonstrated by the example of a Mg-Al-Ca
alloy
given below. It is noted that Al and Ca are both eutectic-forming with Mg, and
form
these eutectics at 33 mass% and 16.2 mass% of the element, respectively. These
values should be compared with the eutectic value of 23.5 mass% for Ni, which
is
midway between these two.
Note that in all the examples presented below, alloy compositions and EPH
values are
expressed in mass% values, unless otherwise stated. The data described in the
examples is also tabulated in Table 3 for ease of comparison.
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Example 1
Mg-5mass%AI-3mass%Ca alloy (without Na and with a nominal addition of 2000
parts
per million by mass [that is, 2000 ppm or 0.2 mass%] of Na) was melted and
cast into a
metallic mould and then tested for hydrogen storage properties. This alloy
contains a
comparable total mass% of eutectic elements (in this case, 8 mass%) as a
commercial
Mg-Ni alloy, and based on the eutectic compositions should also form a similar
amount
of eutectic and intermetallic compounds as the commercial Mg-Ni alloy.
The alloy without Na addition performed extremely poorly with an activation
time of 15
hours and a cyclic EPH value of 1.1 mass% H2. This was improved with the
nominal
addition of 2000 ppm Na yielding a shortened activation time of 8 hours and an
increased cyclic EPH value of 3.7 mass%. Although this demonstrates a clear
positive
benefit for a Na addition to an otherwise poor alloy, the improved values
still fall well
short of a high performance alloy with a zero activation time and an EPH value
of
approximately 6.5 mass% H2.
It is evident from this example that it is not simply a matter of arbitrarily
picking a
eutectic element, or combinations of eutectic elements, and then randomly
choosing an
addition amount(s) to obtain improved hydrogen storage characteristics in an
Mg-based
alloy. Rather, a substantial degree of inventiveness is required in order to
identify and
optimise superior alloy compositions. The inventiveness flows from determining
and
understanding the features that individual elements and combinations of
particular
elements contribute to hydrogen storage performance and other process-related
and
application-related parameters.
This patent application discloses an improved set of Mg-based hydrogen storage
alloys
that are carefully prepared using selected amounts of subsets of the
aforementioned
eutectic forming elements, sometimes in conjunction with Na added as a
performance-
enhancing element. These alloys are described and illustrated in examples in
more
detail below.
Cu added to Mg
As noted in an earlier section, the main effect of Cu in Mg is to improve the
kinetics of
hydrogen activation, hydrogen absorption rate and hydrogen desorption rate
over that of
pure Mg. It is believed that Cu does this by acting as a catalyst that
facilitates the
breakdown of hydrogen gas into hydrogen atoms and facilitates the transport of
those
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atoms into the Mg where they react and form as solid hydrides, for example,
MgH2. In
addition, Cu provides a layered eutectic structure of Mg and Mg2Cu
intermetallic that
surrounds and interpenetrates the primary Mg grains and which provides easy
transport
paths for hydrogen atoms to reach their reaction sites, which may be with
primary Mg
grains or with the Mg2Cu intermetallic constituent in the eutectic.
We have observed that Cu is similar in effect to Ni (a well-known addition to
Mg for
hydrogen storage purposes) but that its performance is asymmetric with respect
to Ni.
In particular, Cu provides an improved overall rate of hydrogen absorption
after the first
hour compared to a similar mass% addition of Ni, even though Ni displays a
more
accelerated initial stage of absorption (Figure 4). However, Cu shows a slower
rate of
hydrogen desorption compared to a similar mass% addition of Ni, but it does
this with
no loss of EPH storage capacity. Since Cu is a lower cost element than Ni, it
is clear
that Cu may be beneficially used rather than Ni for applications in which the
desorption
rate is less critical than the absorption rate.
We have further found that the addition of Na to Mg-Cu alloys (Mg-5.2%Cu, Mg-
14%Cu,
Mg-20%Cu) enhances the hydrogen storage characteristics, in particular,
providing
consistent improvements in effective peak hydrogen levels (to values as high
as 6.3%).
It also improves cycling kinetics, and in general reduces the activation time
for hydrogen
absorption to commence. It is specifically found that Na substantially
improves
hydrogen desorption rates during cycling (thus ameliorating the slower
desorption rate
noted above for binary Mg-Cu alloys), compared to Mg-Ni alloys in which Na
additions
tend to improve the hydrogen adsorption rate instead.
Example 2
Mg-5.2%Cu alloy has been tested and found to have an EPH value of 4.3% under
the
previously noted conditions. The nominal addition of 2000 ppm of Na to the
alloy
significantly raises the EPH of the alloy to 6.4%, a highly acceptable and
commercially-
useful level.
Si added to Mg
Although Cu, Ni and Si are each eutectic-forming elements with Mg, silicon
differs from
Cu and Ni in that it is both lightweight and cheap, and also exhibits its
eutectic point at a
very low addition level, 1.3% Si. This means that a high proportion of
eutectic structure
can be achieved with relatively small additions of silicon. Such a
microstructure has
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large amounts of interfacial area between the phases through which hydrogen
transport
can easily take place.
In addition, by exceeding 1.3% Si, the formation of primary Mg2Si
intermetallic phase
particles can be facilitated should this be considered a desirable structural
feature to
further increase options for hydrogen transport pathways. This latter device
is not
possible in Mg-Cu or Mg-Ni alloys without adding significantly larger amounts
(greater
than 32% and greater than 23.5%, respectively) of these heavy elements. We
have
found that the addition of even relatively small amounts of Si to the alloy,
for example,
approximately 0.2%, also improve the chip formation process achieved during
mechanical processing of the alloy, which is a significant processing benefit.
As a sole addition, Si is not as effective in as Cu or Ni in shortening
activation time or in
increasing absorption or desorption rates. However, the addition of Na to Mg-
Si binary
alloy has significant positive impacts on certain performance aspects, as
shown in the
following examples.
Example 3
In a hypoeutectic Mg-0.5%Si alloy, a nominal Na addition of 2000 ppm did not
change
activation time (which remained at 5 hrs), but did improve the hydrogen
cycling kinetics
resulting in an improved multiple cycle EPH value of 5.2% H2 (with Na)
compared to 4.0
(without Na). This improvement was achieved despite the Na addition not
providing any
significant microstructural refinement to the eutectic. This is a surprising
finding given
that microstructural refinement has been generally accepted as the key
mechanism
behind improved performance in eutectic-based alloys. Clearly, Na is able to
provide
benefits for hydrogen storage via more than this one mechanism.
Example 4
There are also measurable benefits of adding Na to Mg alloys with
hypereutectic Si
levels, i.e. above 1.34% Si. For example, for a Mg-1.6%Si alloy, although the
activation
times were still long with a nominal 2000 ppm Na addition (18 hrs compared to
>20 hrs
without Na) the multiple cycle EPH value was dramatically increased from 0 to
5.1% H2
with the addition of Na.
Example 5
Furthermore, we have found that increasing the Si content of the alloy to 2.1
A resulted
in a decreased activation time of 6 hours and an increased cyclic EPH of 2.6%
even
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without addition of Na. When Na is added at nominal 2000 ppm level to the Mg-
2.1%Si
alloy, the activation time dropped to 3 hours and the cyclic EPH rose to 5.5%.
Cu and Ni added to Mg
We have already compared Mg-Cu alloy with the Mg-Ni alloy and shown that Cu
and Ni
exhibit differing responses to their hydrogen absorption and desorption
kinetics. This
surprising observation suggested to us the beneficial use of Mg-Cu as a
replacement for
Mg-Ni in applications where desorption rates were not critical but where cost
was the
more important driver.
From this insight, we have hypothesised, investigated and determined that Ni
can be
added to a Mg-Cu alloy (or vice versa) such that at particular mass%
combinations of
the elements not only are the counter-effects offset, but improved hydrogen
storage
capacity during cycling may be achieved. Our claimed preferred composition
ranges
reflect these findings. In fact, the best hydrogen capacity is achieved at
relatively low
overall alloy addition levels (for example, Mg-4%Cu-1%Ni, compared with
existing
higher levels of Ni used commercially). We can therefore tailor Mg-Cu-Ni alloy
compositions to provide improved properties at potentially reduced alloy
weight and
alloy cost.
We have further found that Na improves the overall performance of Mg-Cu-Ni
alloys,
presumably among other things, by Na acting to improve the reduced hydrogen
desorption rates caused by Cu (thus ameliorating the rate loss noted above)
compared
with Mg-Ni alloys in which Na additions tend to improve the hydrogen
adsorption rate.
We have found that the benefit of Na is conferred especially at particular
mass%
combinations of Cu and Ni additions.
Example 6
It has been determined that a Mg-5.2%Cu alloy (without Na) has a multiple
cycle EPH
value of 4.3% H2. When some of the Cu is substituted by Ni, as in the Mg-4%Cu-
1%Ni
alloy (without Na), the EPH value is improved to 5.1%. A further nominal
addition of
2000 ppm Na to the alloys raises the EPH of the nominal Mg-4%Cu-1%Ni alloy to
6.5%,
which is higher than the EPH values achieved for either the Mg-5.2%Cu alloy
with Na
addition or a Mg-4.7%Ni alloy with Na, which were measured at 6.4% and 6.3%
respectively.
Example 7
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Surprisingly, a nominal addition of 2000 ppm Na to the nominal Mg-4%Cu-1%Ni
alloy
(approximately 5% total alloy content) yields a greater improvement to EPH
value (5.1
to 6.5%) than the same Na addition does to a nominal Mg-3.5%Cu-3.5%Ni alloy
(approximately 7% total alloy content) where EPH is improved from 5.1 to 6.0%.
Not
only does this demonstrate that a leaner composition alloy can have as good a
hydrogen capacity as a richer composition alloy, but that Na clearly has other
positive
effects on EPH that are independent of any beneficial effects that it has on
the Mg-Cu
and Mg-Ni based eutectics present in the structure.
Table 3 ¨ Composition and hydrogen performance data for various Cu-Ni
Compositions
, -------------------------------------
eu-Ni Reiated Comp ton with no Na Cu-Ni Reiated Compositions
with Na Added
Cu Ni Y'. Actvtion E-PÃ14 ......................................
1111.1110111111MEMZE
3.6 (19 4 5,1 ........................................
1111111111111111111101111111111111
5,2 0 7 4,3 ........................................
1111111111111111MIIIIIIIMINIENI
...............................................................................
. 111111111111111111111111
2,6 2.6 5 4,6 ........................................
IIRINIMMIIIIIIIIIIRMENI
............................................... 2.45 O.% 0
1-
0 5 3,4 14 0 i 4 6.0
3,5 K1 5 5,1 ----------------------------------------
111111111111111.11111111011111111.11161
5 2 5,5 ----------------------------------------
IIIEIIMEIMIIIIMIIMIMEIIII
6,8 6,5 1 5,1 ----------------------------------------
IIMUMMEMIIIIMINOMME
1.1111111111.11.1MINEEMENE
,
.k -;;? ).9.9 ': 10 ......................................... ;?
IIIIIIIIIIIMEIMEMEIMEll
, 3,5 0 12 2.7 ........................................
IIIIIIIIIIIIIMIIIIIIMEMEM311
1 5 9 6 4,9
OEIIMIMEIIIIMIIMIIEIEII
11111111111111111111111111111111111111111111
11111111111111111111111111MEIMI
11 0 2 5,3
1.111111111111111101111.1311
0 14 6 5,1 .... 11111111111
10 o 4,7 6 5,1 ........................................
IIIIIIIIIIIIMIIIIIMEEMEM
Cu and Si added to Mg
The addition of Cu and Si together to Mg does not appear to provide any
substantial
improvement to hydrogen storage capacity compared to that achieved in the
simple
binary Mg-Cu or Mg-Si alloys. However, the combination of adding Cu and Si
together
in Mg improves the responsiveness of the alloy to a Na addition and achieves
greater
increase in the EPH values compared to the effect of Na added to either of the
simple
binary alloys, even though it may not achieve the highest EPH value in the
ternary alloy.
This is a surprising result that could not be predicted a priori.
Nevertheless, when the addition of Si to Mg-Cu alloys (particularly where the
amount of
Si added is a direct substitute for some of the Cu content) results in
hydrogen storage
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characteristics that are similar to the binary Mg-Cu alloy then a commercially
attractive
alloy has been formulated. This is because silicon is much cheaper and is much
less
dense than Cu, and is also cheaper than Mg, resulting in a potentially cost-
effective and
weight-effective alloy for less demanding hydrogen storage applications.
This is believed to occur because Si, even at relatively small addition
levels,
dramatically increases the amount of eutectic intermetallic particles present
in the
microstructure thus increasing the interfacial area available for transport of
hydrogen
atoms. It is believed that Na tends to segregate to these interfaces and that
its presence
facilitates the transport of hydrogen to the key reaction and absorption sites
provided by
the primary Mg phase and the Mg-Cu eutectic, rather than the less responsive
Mg-Si
eutectic.
Example 8
As noted above, it has been determined that a Mg-5.2%Cu alloy (without Na) has
a
multiple cycle EPH value of 4.3% H2. When some of the Cu is substituted by Si,
as in
the Mg-4%Cu-1%Si alloy (without Na), the EPH value is decreased to 2.6%.
However, a
nominal addition of 2000 ppm Na to the alloys raises the EPH of the nominal Mg-
4%Cu-
1%Si alloy to 6.2%, which is a substantially greater increase (+3.6%) in EPH
value,
compared to that achieved in Mg-5.2%Cu alloy, that only achieves a +2.1%
increase to
an EPH of 6.4%.
Review of the data for Mg-Cu-Si alloys (Na-added) shows that for copper-rich
alloys
with reducing silicon contents, the EPH reduces significantly as the copper
concentration drops, and this reduction is not arrested even with the addition
of Ni.
Surprisingly, the addition of silicon to form the alloy of this example (Mg-
4%Cu-1%Si
alloy with Na addition) reverses this trend to produce an alloy showing an EPH
of
6.2wt%H2 This may be due to the embrittling effect of the silicon or its
ability to
disproportionately expand the volume of eutectic phase. This alloy has
attractive
performance at a favourable cost, making it commercially attractive.
Table 4 ¨ Composition and hydrogen performance data for various Cu-Si
Compositions
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Cu-Si Related Compositions with no Na Co-Si Related Compositions
with Na Added
,
(..k./ Si N Act'vtion .. E PH4 Cu Si N A cevt ion
EP H 4
+
5.2 0 / ==
4.3 5.2 0 i 3
6,4
3.6 0.75 11 2.6 3-6
INESIMMINWEIMMEM
0 5 3.4
IIICIIIIEIIMIIIIIIIIIEIIIIIESIII
111111111111MMIIIM1011011MPII
2.62 0.3E, a a9 .w ......................................... ::.
1 1111111111111111111111111111
11111110111111010111111111111111111
11111111!11lHIIIIIIIIEill10111
3,5 0 12 2.7 ................ UM 0
111111111111
MEM 2 1111111111111WEI
0 ..... 0.12 3 4.0 0.28 4.5 5.5
0 2.1 6 2,6 2,06 3 5,5
0 0.52 5 4.0 ................. MEM 0.52
111111111111111111
1 1,2 2
5.2
0 1,6 >20 0.0 0 1.6 18 5.1
11 0 2 5.3 24 0 2 4',7
Ni and Si added to Mg
The addition of Ni and Si together to Mg differs from the combined effect of
Cu and Si
additions noted above. There appears to be little gain in adding Si at small
amounts to
5
alloys with Ni contents in the higher range, for example, about 5%; however,
there are
distinct gains when Si is added to alloys with lower Ni contents in the 1%
range. We
believe that this is due to fact that Mg-Ni eutectics, even in the absence of
Na, are more
potent than Mg-Cu eutectics in terms of their catalytic capability, therefore
when the Ni
content is high the addition of Si adds little to the alloy's hydrogen storage
capacity. We
10 further contend that when the amount of Mg-Ni eutectic is reduced as in
a low Ni
content alloy, a Si addition, even at low levels, is able to exert its very
positive influence
by forming large amounts of Mg-Si eutectic that open up pathways for hydrogen
atom
transport within the Mg grain structure (Figure 6).
It appears that the direct substitution of Si for Ni will be possible in Mg-Ni
alloys without
substantial loss of hydrogen storage performance, and also that there may
opportunities
to reduce the total Ni plus Si alloy content as well, while maintaining
adequate hydrogen
storage characteristics for certain applications. As above, Si is much cheaper
and
lighter than Ni, and is also cheaper than Mg; therefore both of the above
options will
lead to a cheaper and lighter alloy that suits particular hydrogen storage or
transportation applications that would otherwise be unavailable to higher Ni
content
alloys. This is true even for Si additions that are in the hypereutectic
range, that is,
greater than 1.3%.
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As for the Mg-Cu-Si alloys described above, the addition of Na appears to
exert greater
beneficial effects in particular regions of the composition window for Mg-Ni-
Si alloys. For
example, the addition of Na appears to yield greater improvements to lower Ni
content
alloys than to higher Ni content alloys. This is believed to be because of the
inherently
greater catalytic effect of Ni than Si thus partially negating the benefit of
Na addition.
Example 9
The addition of approximately 0.8% Si (a hypoeutectic amount) to a Mg-1.3%Ni
alloy
containing a further nominal addition of 2000 ppm Na increases the effective
peak
hydrogen storage level after cycling from 3.5 to 5.3%, a useful though modest
level.
This should be compared with a cyclic EPH value of 5.9% for a Na-containing Mg-
5.3%Ni-0.4%Si alloy.
Example 10
We have found that a nominal Mg-1.6%Si-1%Ni alloy, that is containing a
hypereutectic
amount of Si, has an activation time of 6 hours and multiple cycle EPH value
of only
1.6wt%, a low level. However, the nominal addition of 2000 ppm Na to the alloy
reduces
activation time to 3 hours and raises the multiple cycle EPH value to 5.8wt%,
a
commercially attractive level for certain applications. By comparison, a
simple binary
hypereutectic Mg-1.6%Si alloy displays an EPH of 0% before Na addition, and an
EPH
of 5.1 A after Na addition, but with very long activation time of greater than
20 hours and
18 hours, respectively.
Table 5 ¨ Composition and hydrogen performance data for various Cu-Ni
Compositions
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NI - Si Related Compositions with tlo Na NI - Si Related
Compositions with Na Added
1
Ni wt% Si wt% :.=.; ,,,,,-t% Actsition i EPH4 --------------------------------
---- INENEEMEMBE Act:vtionirEll
i
4,7 0 6 i 5,1 4.7 i 0 v
6.3
+
6. 4 0,2
+
1 1.6 6 i 1.6 1 i 1.5 3
5.8
2.62 10 2.1
IIIIBIMIASIIIIIEIIIIIIIIIIIIIIIIIIIII
iiiiiiiti
...............................................................................
... IIEIIMIEIIEIIIIIIIIIIIIIIIIIMIIIIM
14 0 . , 6 5,1 ------------------------------------
---- 1111,1=1111111111111111103311
0 0.12 3 i 4,0 0'i .28 4.5
5.5
+
0 2,1 6 i 2,6 0=i 2 06
+
1,1 i 0,84 8
5.3
i
1 0,2 12 2,6 1
0.2 MEI 5,3
0 , 062 S 4.0 ....... 0 062
5.2
0 1,6 , >20 0,0
IIIMIIMIMEIIIIIIIII 18 11111W
.
...............................................................................
. IIEIIIIMIIIIIOMIIIIIIIIIIIIIIIIIIIIIIIIIIIII
..
, 2.58 i 0 4
43
+
4 i 1 3
4.3
+
1.3 i 0 3.5
3.5
Cu, Ni and Si added to Mg
The effects of a combined addition of Cu, Ni and Si into Mg (a quaternary
alloy) are
complex and result in interesting and useful changes to activation kinetics.
In addition,
there are clear benefits of adding Na to the quaternary alloys with strong
improvements
in both activation kinetics and overall storage performance observed.
Example 11
A nominal Mg-2.5%Cu-1%Ni-0.4%Si alloy without Na addition shows an activation
time
of 10 hours and a cyclic EPH value of 2.1% H2. When a nominal addition of 2000
ppm
Na is made, the alloy shows an improved activation time of 3 hours and an
improved
EPH of 5.8%.
If the same Na-containing quaternary alloy is compared with the Na-containing
Mg-
1.3%Ni-0.8%Si alloy from Example 9, it can be seen that there is an
improvement in
cyclic EPH value in the quaternary alloy compared to the ternary alloy, that
is 5.8%
compared to 5.3%.
If the same Na-containing quaternary alloy is compared with a Na-containing Mg-
2.5%Cu-1%Ni ternary alloy, there are improved activation kinetics despite an
increased
activation period (3 hours activation, and saturation hydrogen value at 20
hour of 5.4%)
compared to the Si-free ternary alloy (0 hours activation, saturation hydrogen
value of
5.0%). Note: this data is not shown in Table 3. As such, the Mg-2.5%Cu-1%Ni
alloy with
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Na is attractive for its favourable EPH performance, but the addition of the
0.4%Si can
make the alloy cheaper and improve the activation performance.
As noted previously, Si is much cheaper and lighter than either Cu or Ni, and
is also
cheaper than Mg. Cu is also cheaper than Ni. Therefore any direct substitution
of Si or
Cu for Ni that is possible, or any reduction in total alloy content, will lead
to a cheaper
and lighter alloy.
Table 6 ¨ Composition and hydrogen performance data for various Cu-Ni-Si
Compositions
Cu-N1-5i Related Corn sitions with no Na Cu-Ni-Si Related
Compositions with Na Added
C Ni Si C S ActVtion
EPH4
2.6 1 14 10 2.1 2.6 1 (1.4 3
5.8
1 1 02 3 i 3.8 1 1 0.2 2
4.9
1 1 2 Not measured 3.4
........................ 1111111111111=111111111111111111111111
Further Examples
Example 12
Review of the data for Mg-Ni-Si alloys (Na-added) shows that for alloys
consisting of
only Mg and Si with Na, the EPH values decrease with increasing Si. However,
surprisingly, the increase is reversed at Mg-4.5%Si with Na addition; this
alloy shows
5.8wt%H2. The light weight of the silicon combined with an extensive network
of
primary Mg2Si may be combining to create this effect. As noted, Si is cheaper
than Mg,
so the cost of the alloy is actually decreased at this relatively high
addition, making it a
commercially attractive.
Summary
It will be understood that the invention disclosed and defined in this
specification
extends to all alternative combinations of two or more of the individual
features
mentioned or evident from the text or drawings. All of these different
combinations
constitute various alternative aspects of the invention.
Table 3 ¨ Composition and hydrogen performance data for examples 1 -11 above
Nominal alloy composition
Example Nominal Activation Cyclic
EPH
(mass % of elements; balance
No. Na (ppm) time (hr) (mass %)
Mg)
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0 15 1.1
1 5 Al, 3 Ca
2000 8 3.7
0 7 4.3
2 5.2 Cu
2000 3 6.4
0 5 4.0
3 0.5 Si
2000 5 5.2
0 >20 0
4 1.6 Si
2000 18 5.1
0 6 2.6
2.1 Si
2000 3 5.5
0 4 5.1
6 4 Cu, 1 Ni
2000 0 6.5
0 5 5.1
7 3.5 Cu, 3.5 Ni
2000 2 6.0
0 11 2.6
8 4 Cu, 1 Si
2000 3 6.2
0 >20 3.5
1.3 Ni, 0.8 Si
9 2000 8 5.3
5.3 Ni, 0.4 Si 2000 3 5.9
0 6 1.6
1 Ni, 1.6 Si
2000 3 5.8
0 10 2.1
11 2.5 Cu, 1 Ni, 0.4 Si
2000 3 5.8
0 Not Tested Not Tested
12 4.5 Si
2000 7 5.8
24
